Unraveling the role of telomeres and telomerases in the response to neurotoxicants

Background: Telomeres are repetitive DNA sequences that protect chromosome ends and whose length is maintained by telomerase activity [1]. While telomere dynamics are well characterized in proliferating cells, their role in post-mitotic cells such as neurons remains poorly explored [2]. Particularly, the impact of telomere attrition or telomerase dysfunction on the cellular response to neurotoxicants is largely unknown. Objective: We aimed to investigate whether telomere shortening increases the susceptibility of neuronal cells to the toxic effects of common environmental neurotoxicants (i.e., HgCl2, acetaldehyde). Methods: The effects of HgCl2 (0-100mM) and acetaldehyde (0-10mM) on the metabolic activity (MTT reduction assay) and lysosomal integrity (Neutral Red uptake) of SH-SY5Y human neuroblastoma cells were assessed by determining IC10 and IC50 for each neurotoxicant. These assessments were performed either 24h after exposure to the neurotoxicants or following a 72h pre-treatment with 1mM XAV939, a tankyrase-1 inhibitor that limits telomerase access to telomeres, promoting telomere shortening [3]. Relative telomere length in XAV939-treated treated alone and in combination with biologically relevant, subtoxic concentrations of HgCl2 (10 and 25 mM) or acetaldehyde (0.1 and 5 mM) was measured using quantitative real-time PCR. Results: Our findings revealed that HgCl2 and acetaldehyde reduced the metabolic activity and lysosomal integrity of SH-SY5Y cells in a concentration-dependent manner. Also, HgCl2 shifted the IC10 from 26 to 15 mM for metabolic activity and from 21 to 6 µM for lysosomal integrity in XAV939-treated cells, compared to cells not exposed to XAV939, suggesting that shortened telomeres may have increased the cells’ susceptibility to HgCl2. In turn, XAV939 pretreatment did not alter the impact of acetaldehyde on those parameters. Notably, XAV939-induced telomere shortening was confirmed by qPCR analysis. Interestingly, our data showed that 100µM acetaldehyde and 10 µM HgCl₂ reduced the cells’ telomere length to 45% and 77% of control levels, respectively, at the same time point. Conclusions: Our preliminary findings suggest that telomere shortening increases SH-SY5Y cells vulnerability to the toxic effects of HgCl₂, evidencing a possible involvement of telomere-related mechanisms in the response to neurotoxicants. However, further research is required to confirm the importance of such mechanisms in neurotoxicity-related responses.